09-24-2021-1322 - The short laser pulse knocked out core L-shell electrons without breaking the crystalline structure of the metal, making it transparent to soft X-rays of the same wavelength for about 40 femtoseconds.[13][14][non-primary source needed]

 

Mechanisms and examples of saturable absorption[edit]

Absorption saturation, which results in decreased absorption at high incident light intensity, competes with other mechanisms (for example, increase in temperature, formation of color centers, etc.), which result in increased absorption.^[3][4] In particular, saturable absorption is only one of several mechanisms that produce self-pulsation in lasers, especially in semiconductor lasers.^[5]

One atom thick layer of carbon, graphene, can be seen with the naked eye because it absorbs approximately 2.3% of white light, which is π times fine-structure constant.^[6] The saturable absorption response of graphene is wavelength independent from UV to IR, mid-IR and even to THz frequencies.^[7][8][9]In rolled-up graphene sheets (carbon nanotubes), saturable absorption is dependent on diameter and chirality.^[10][11]

Microwave and terahertz saturable absorption[edit]

Saturable absorption can even take place at the microwave and terahertz band (corresponding to a wavelength from 30 μm to 300 μm). Some materials, for example graphene, with very weak energy band gap (several meV), could absorb photons at Microwave and Terahertz band due to its interband absorption. In one report, microwave absorbance of graphene always decreases with increasing the power and reaches at a constant level for power larger than a threshold value. The microwave saturable absorption in graphene is almost independent of the incident frequency, which demonstrates that graphene may have important applications in graphene microwave photonics devices such as: microwave saturable absorber, modulator, polarizer, microwave signal processing, broad-band wireless access networks, sensor networks, radar, satellite communications, and so on.^{[12][non-primary source needed]}

Saturable X-ray absorption[edit]

Saturable absorption has been demonstrated for X-rays. In one study, a thin 50 nanometres (2.0×10⁻⁶ in) foil of aluminium was irradiated with soft X-ray laser radiation (wavelength 13.5 nm). The short laser pulse knocked out core L-shell electrons without breaking the crystalline structure of the metal, making it transparent to soft X-rays of the same wavelength for about 40 femtoseconds.^{[13][14][non-primary source needed]}

See also[edit]

• Two-photon absorption

https://en.wikipedia.org/wiki/Saturable_absorption